Field of the Invention
The invention relates to materials used in medical implants. More particularly, the invention relates to a biocompatible material suitable for use in high-cycle flexural applications including artificial heart valves.
Background
Artificial heart valves preferably should last at least ten years in vivo. To last that long, artificial heart valves should exhibit sufficient durability for at least four hundred million cycles or more. The valves, and more specifically heart valve leaflets, must resist structural degradation including the formation of holes, tears, and the like as well as adverse biological consequences including calcification and thrombosis.
Fluoropolymers, such as expanded and non-expanded forms of polytetrafluoroethylene (PTFE), modified PTFE, and copolymers of PTFE, offer a number of desirable properties, including excellent inertness and superior biocompatibility, and, therefore make ideal candidate materials. PTFE and expanded PTFE (ePTFE) have been used to create heart valve leaflets. It has been shown, however, that PTFE stiffens with repeated flexure, which can lead to unacceptable flow performance. Failure due to formation of holes and tears in the material has also been observed. A variety of polymeric materials has previously been employed as prosthetic heart valve leaflets. Failure of these leaflets due to stiffening and hole formation occurred within two years of implant. Efforts to improve leaflet durability by thickening the leaflets resulted in unacceptable hemodynamic performance of the valves, that is, the pressure drop across the open valve was too high.
As such, it remains desirable to provide a biocompatible artificial heart valve design that lasts beyond ten years in vivo by exhibiting sufficient durability for at least about four hundred million cycles of flexure or more.